Radio receiver



Dec. 1, 1936.

E. L. KOCH RADIO RECEIVER Filed April 16, 1931 INVENTOR EARL L. KOCH.

ATTORNEY Patented Dec. 1, 1936 UNITED STATES RADIO RECEIVER Earl L.Koch, Chicago, Ill., assignor, by mesne assignments, to Radio PatentsCorporation, New York, N. Y., a corporation of New York ApplicationApril 16, 1931, Serial No. 530,555

7 Claims.

This invention relates to improvements in radio receivers; especially ofthe kind used in broadcasting, with a loud speaker attached.

An object of the invention is to provide a radio receiver containing anovel form of vacuum tube so connected that the receiver can beexceedingly simple in design and quite inexpensive to produce.

A further object is to provide a radio receiver wherein the vacuum tubesof the various stages are all of the external-grid type, of restricteddimensions, but relatively large output; and low in the cost of bothmanufacture and operation.

Another object of the invention is to provide a radio receiver of thischaracter having vacuum tubes of such construction and arrangement thatthe grid of each tube can be operated at the same steady direct currentpotential as the anode of the preceding tube; so that the usual gridblocking condenser may be omitted, and the various tubes can all beunited by direct impedance coupling.

A still further object is to provide a radio receiver of such designthat the filaments of all the vacuum tubes including the detector can beenergized with alternating current derived from any convenient source.

An additional object is to provide a radio receiver which can beutilized with any sort of telephone or loud speaker, but which ispreferably adapted to be employed with an electrostatic loud speakerwith a source of polarizing voltage.

These and other objects and advantages will be more fully set forth inthe following description, taken with the drawing, which illustrates oneof the many possible embodiments of the principle of my improvedreceiver. This disclosure, however, is illustrative only, and thedetails of structure and function may be varied, without exceeding thescope and spirit of the invention, as defined by the broad and specificmeanings of the terms in which the appended claims are expressed.

The drawing shows in diagrammatic outline a radio receiver having thecharacteristics of my invention.

Numeral I indicates a receiving antenna connected to a radio frequencycoupling stage comprising a vacuum tube 2 consisting of a glass orsimilar container housing a cathode of the heated variety and acooperating anode; but with the grid on the exterior of the containerand united directly with the antenna I. A second radio frequency tube 3is coupled to the tube 2 via a selector circuit which will be describedmore in detail later. Audio frequency tubes are indicated at 4 and 5,with a gas-filled detector at 6.

The tubes 3, 4, 5 and 6 are all like the tube 2 with outside grids; andthe receiver thus includes two stages of radio frequency amplification,and two stages of audio frequency amplification, with the detector 6between the stages. At I is a volume control device comprising apotentiometer resistance in the antenna, with an adjustable connectionto the grid of the tube 2.

To energize the filaments of the tubes abovementioned, alternatingcurrent is led through mains 8 to the primary coil 9 of a suitabletransformer, having a secondary II] to which allthe filaments, includingthat of the detector 6, are

joined in parallel. The same transformer has another secondary windingII, connected to the filament of a two-element vacuum tube half-waverectifier I2. A third secondary winding I3, of v the transformer has oneof its terminals con- 20 nected to the anode of this rectifier; so that,as subsequently explained, the plates or anodes of all the tubes 2, 3,4, 5 and 6 may be supplied with direct current. The filament of therectifier is connected through a lead I4 to'a. common conductor I5, towhich the anodes of the tubes 2, 3, 4 and 5 are all united in multiple.The lead I4 may contain a suitable inductance I6. A conductor I'I,joined to the antenna I, is united at its other extremity through theconductor I8 to the remaining terminal of the secondary I3; and acrossthe secondary I0, is placed a resistance I9 united to the conductor I8at its middle. The connections from the conductor I5 to the plates ofthe tubes and the conductor II are bridged by suitable condensers 20;and across the leads I4 and I5 is a condenser 2I to cooperate with theinductance I6 and smooth out the unidirectional current produced by therectifier I2. All of the connections to the plates of the vacuum 6'tubes 2, 3, 4, 5 and 6 include impedance in series, and the anodecircuit of the detector may also contain a small resistance 22. T

The grids of the tubes 4, 5 and 6 are each directly connected with theplate of the preceding tube; and as each grid is insulated by thematerial of the container from the filament and anode associatedtherewith, no grid blocking condenser or coupling transformer isrequired.

Each grid will be at the same direct current potential as the plate ofthe preceding tube, so

that direct aperiodic impedance coupling can be utilized in both theradio and audio stages. I

Between the tubes 2 and 3 is a selector circuit or lumped tuning unitcomprising a pair of 5 loosely coupled coils 23, each in a series with avariable condenser 24. These condensers are in parallel, having a commonground at 25. The grid of the tube 3 is united to one of the coils 23and the adjacent condenser 24, the other coil 23 being in series withone of a pair of loosely coupled coils 26, the other of which is inseries with the plate of the tube 2. The coils 23, with the coil 26 inseries with one thereof, are connected to the conductor l1 as shown.With the tube 2 interposed, antenna reactions are prevented frominfluencing the tuned selector circuit.

The plates of the tubes 3, l, 5 and 6 may all have suitable impedancesin the connections between them and conductor 15. All the plates operateat the same steady potential, eliminating the need of voltage dividers;and only one filament winding I0 is needed for all the tubes. Hence thecurrent needed is small, and the rectifier [2 may be small. The absenceof C bias on the grids further simplifies the problem of supplying powerto the tubes.

A loud speaker of the static description is illustrated at 21. Toprovide polarizing voltage, a small two-element vacuum tube rectifier isshown at 28. Across the mains 8 is another transformer primary coil 29,with one secondary 30 connected to the anode of the rectifier 28, andanother secondary 3| to energize the oathode thereof. The other terminalof the coil 30 is united to a large resistance 32, in series with a muchlarger resistance connected to one terminal of the loud speaker. Betweenthis terminal and the plate of the tube 5 is a suitable condenser 34.The other terminal of the loud speaker is of course joined to thenegative terminal of the rectifier 28. In parallel with the loud speakerand rectifier 28 is a filter condenser 35. A connection may be placedbetween the lead to the plate of the tube 5, and a point between theresistances, if desired. These resistances 32 and 33 may have values of150,000 and 500,000 ohms respectively.

The rectifier 28 will supply approximately 500 volts across the speaker;but, as the condition is a static one, no current at all is requiredonce the condenser 35 is charged. Therefore, the rec tifier and thetransformer can be very small. Any type of speaker other than anelectrostatic one may be used if preferred.

The receiver as above described is thus constructed around tubes of theexternal-grid type and affords several important advantages. Thesimplicity of circuit arrangement is obvious and makes possible themanufacture of a receiver at extremely little expense. Also thearrangement shown utilizes but two radio frequency stages, a detectorand two audio frequency stages; and in respect to number of tubes used,is quite comparable to the average broadcast receiver of today.

With regard to the external-grid, considering first the tube itself, itis equal in performance to existent types of screened-grid tubes, butmuch simpler. It contains in the bulb but two elements, the filament andthe plate. Tubes of this type may be manufactured quite as cheaply asincandescent automobile lamps. The gridhas merely the form of a metallicsheath around the outside of the bulb.

Such a tube makes possible the operation of the filament directly froman alternating current source without necessity of resorting toindirectly heated cathodes. This statement holds true of tubes used inall positions of the set.

Comparing this construction with the present type of indirectly heatedcathode screen-grid tube, the cost of the external grid-tube isnegligible.

Due to the fact that the grid is insulated from the electron stream, theusual grid blocking condenser or transformer coupling may be dispensedwith. Examination of the drawing shows, as above stated, all grids to beat the same steady D. C. potential as the plate of the preceding tube,allowing the use of direct impedance coupling in both the radio and theaudio stages.

Aside from the question of simplicity and economy the tube itself, for alarge output, can be made physically much smaller than previous tubes.In view of the present trend toward small or so called midget sets, thequestion of size is important. Unquestionably, a receiver constructedaccording to this invention can, for the same performance, be made muchsmaller and more cheaply than existing sets.

The detector and all other tubes are impedancecoupled, and the couplingunits are simply choke coils which, due to the small current carried,are of Very small dimensions. These choke coils are connected from theplates of the tubes to the conductor [5.

The radio frequency and the audio frequency amplifier tubes are hardtubes; the detector being of the soft variety, but it is to beunderstood that all of the tubes may be made of the soft or gas filledtype with slight changes in the structure of the same design.

What is claimed is:

l. A radio receiver comprising amplifier tubes and a detector tube, eachof said tubes comprising an electrically heated cathode a plate and anexternal grid, means for heating the cathodes of all the tubes andmaintaining them at a common potential, including said detector tube,with alternating current, a conductor connecting the plate of some ofsaid tubes directly to the grid of a following tube, and a loadimpedance between said conductor and a source of direct current formaintaining said plate and said gridv at the same potential and polarityrelative to the respective cathodes.

2. A radio receivercomprising radio frequency and audio frequencyamplifier tubes and a detector tube, each of said tubes having aninternal anode and cathode with anexternal grid, connections for heatingand maintaining at a common potential the cathodes of all the tubesincluding the detector tube with current from an alternating source, aconductor connecting the plate of a radio frequency amplifier tube withthe grid of a detector tube, a second conductor connecting the plate ofsaid detector tube to the grid of an audio amplifier tube, a highfrequency choke connected between said first conductor and a source ofdirect current for maintaining the plate and grid con-'- nected theretoat an equal potential, and a low frequency choke connected between saidsecond conductor and said source of direct current for maintaining theplate and grid connected thereto at an equal potential relative to therespective cathodes associated therewith.

3. A radio receiver comprising radio frequency, detector and audiofrequency amplifier tubes, each of said tubes comprising a cathode andan anode, with a grid cooperating therewith, the grid of each tube beingdirectly connected to the anode of a preceding tube,. means formaintaining the cathodes of said tubes at a common potential, and meansfor impressing a direct current potential on said anodes via a chokecoil so that the potential of any grid and the anode connected theretois the same relative to the respective cathodes.

4. A radio receiver having vacuum tubes in cascade, each tube containingan anode and a cathode, with a grid on the exterior of the tube, theplate of one tube being connected with the grid of the next succeedingtube, means for maintaining the cathodes of said tubes at a commonpotential, and a source of direct current to impress a potential via animpedance on said plate and grid, the potentials on said plate and gridbeing equal relative to the cathodes associated therewith.

5. A radio receiver having in combination radio frequency amplifiertubes, audio frequency tubes, an intermediate detector tube, each ofsaid tubes including a cathode, means for maintaining said cathodes at asubstantially common potenial, a tuning element between the first radiotube and the next succeeding tube, a conductor connecting a plate of oneof said radio frequency amplifier tubes to a control grid of thedetector tube, a second conductor connecting a plate of the detectortube to a control grid of an audio amplifier tube, a high frequencychoke connected between said first conductor and a source of directcurrent for maintaining the plate and grid connected thereto at an equalpotential, and a low frequency choke connected between said secondconductor and the source of current for maintaining the plate and gridconnected thereto at an equal potential and polarity relative to saidcathodes.

6. A radio receiver having vacuum tubes comprising radio frequency andaudio frequency amplifiers and. an intermediate detector tube, means forenergizing the cathodes and anodes of said tubes from a source ofalternating current and maintaining said cathodes at a common potential,said means including a small rectifier, the grids of each tube beingexterior to the tubes, means for connecting the grid of one tube to theplate of a preceding tube for maintaining the same at a like potentialrelative to said common potential, and a choke coil forming a directaperiodic impedance coupling between an interconnected grid and plateand the output of said rectifier.

'7. A radio receiver comprising vacuum tubes connected in cascade, eachof said tubes comprising a filamentary cathode, an anode and a grid,means for commonly energizing and maintaining at a common potential allsaid cathodes so as to provide a source of free electrons within thetube, the plate of one tube being directly connected to the grid of thefollowing tube, each plate being fed from a source of direct currentthrough a suitable coupling impedance, each interconnected grid andplate being of the same potential and sign with respect to the cathodesource.

EARL L. KOCH.

